Creating a diamond pattern using loops

Question

I am trying to write a program that reads an integer and displays, using asterisks, a filled diamond of the given side length. For Example, if the side length is 4, the prog

Answer 1

How about the following:

side = int(input("Please input side length of diamond: "))

for x in list(range(side)) + list(reversed(range(side-1))):
    print('{: <{w1}}{:*<{w2}}'.format('', '', w1=side-x-1, w2=x*2+1))

Giving:

     *
    ***
   *****
  *******
 *********
***********
 *********
  *******
   *****
    ***
     *

So how does it work?

First we need a counter that counts up to side and then back down again. There is nothing stopping you from appending two range lists together so:

list(range(3)) + list(reversed(range(3-1))

This gives you a list [0, 1, 2, 1, 0]

From here we need to work out the correct number of spaces and asterisks needed for each line:

  *        needs 2 spaces 1 asterix
 ***       needs 1 space  3 asterisks
*****      needs 0 spaces 5 asterisks

So two formulas are needed, e.g. for side=3:

x   3-x-1   x*2+1
0   2       1
1   1       3
2   0       5

Using Python's string formatting, it is possible to specify both a fill character and padding width. This avoids having to use string concatenation.

If you are using Python 3.6 or later, you can make use of f string notation:

for x in list(range(side)) + list(reversed(range(side-1))):
    print(f"{'': <{side - x - 1}} {'':*<{x * 2 + 1}}")